Articulated chain assembly

ABSTRACT

IMPROVED ARTICULATED CHAIN ASSEMBLY FOR A TRACK-TYPE VEHICLE WHEREIN MID-PITCH DRIVING LUGS ARE LOCATED ON THE ASSEMBLY SUBSTANTIALLY EQUIDISTANT THE CENTERS OF THE ARTICULATED JOINTS, AND WHEREIN SAID LUGS HAVE A GEOMETRIC   RELATIONSHIP RELATIVE TO A DRIVING SPROCKET TO PERMIT LIMITED ROCKING OF THE ASSEMBLY ON SAID SPROCKET.

F. E. SIMPSON L ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet1 Filed Sept. 1967 INVENTORS FRED E; SIMPSON EUGENE J. HNILICKA Roy EMAYO 'JOHN S. RICCA JR. GAIL G. AVERY CHARLES E. WAGAMAN F. E. SIMPSONETAL 3,567,294

ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet 1 Filed Sept.20. 1967 -INVENTORS FRED E SIMPSON EUGENE J. HNILICKA Rov E MAvo JOHN S.RlccA JR. CHARLES E. WAGAMAN M1 ATTORNE s GAIL G. AVERY Mflch Z, 9 F.SIMPSON A 3,567,294

ARTICULATED CHAIN ASSEMBLY Filed Sept. 20. 1967 e Sheets-Sheet sISVENTORS A OF FRED ESIMPSON EUGENE .HNILICKA BUSH'NG ROY E. MAYO JOHNS. RlccA JR. GAIL G. AVERY CHARLES EWAGAMAN March 2, 1971 E, SI S ETAL3,567,294 7 ARTICULATED CHAIN ASSEMBLY 6 Sheets-Sheet 4 Filed Sept. 20.1967 INVENTORS EUGENE/1U. HNILICKA JOHN S RlccA JR. CHARLES E. WAGAMAN a0 1 'fimg E?S FRED E. SIMPSON Rov E. MAYO GAIL G. AVERY Mad! 1 1 F. E.SIMPSON L 3,567,294

ARTICULATED CHAIN ASSEMBLY 6 Sheets-Sheet 5 Filed Sept. 20. 1967 ENTORSHNILICKA JOHN S. RICCA JR. GAIL G. AVERY INV FRED E. Suw som EUGENE J.Rev E. MAvo CHARLES E WAGA MA N BY 7") ?i"" {,A. T'FBRNJS F. E. SIMPSONETAL 3,567,294

ARTICULATED CHAIN ASSEMBLY March 2, 1971 6 Sheets-Sheet 6 Filed Sept.20. 1967 E A LE .18

INVENTORS EUGENE J. HNILICKA JOHN S. RICCA JR. CHARLES E. WAGAMAN FREDE. SIMPSON Rev E. MAYO GAIL G- AVERY ATRRNE S United States Patent O M3,567,294 ARTICULATED CHAIN ASSEMBLY Fred E. Simpson, Washington, andEugene J. Hnilicka, Peoria, Ill., Roy E. Mayo, Santa Barbara, Calif.,and John S. Ricca, Jr., Bartonville, and Gail G. Avery and Charles E.Wagaman, Peoria, 111., assignors to Caterpillar Tractor Co., Peoria,Ill.

Filed Sept. 20, 1967, Ser. No. 669,218 Int. Cl. B62d 55/20 US. Cl.305-57 13 Claims ABSTRACT OF THE DISCLOSURE Improved articulated chainassembly for a track-type vehicle wherein mid-pitch driving lugs arelocated on the assembly substantially equidistant the centers of thearticulated joints, and wherein said lugs have a geometric relationshiprelative to a driving sprocket to permit limited rocking of the assemblyon said sprocket.

BACKGROUND OF THE INVENTION This invention relates to an improvedarticulated drive chain assembly for a track-type vehicle, such as acrawler tractor. More particularly, the invention relates to anarticulated drive chain assembly having a driving lug locatedsubstantially equidistant the centers of the articulated joints,referred to as mid-pitch, wherein the lug is formed to cooperate with achain driving sprocket or sprockets to permit limited rocking of theassembly on the sprocket to thereby reduce horsepower losses in thechain drive and to simultaneously limit external wear at the articulatedjoints.

Prior art articulated chain drive assemblies are in general constructedsuch that the articulated joints provide fo two important functions.Firstly, the articulated joints provide hinged connections betweenadjacent chain sections so that the chain, under driving conditions, mayconform to either a linear path or a curvilinear path (i.e. whentraveling on the sprocket or over rough terrain). Secondly, theaticulated joints of prior art structures provide a drive means forco-action wtih the sprocket teeth whereby the chain is forcefully drivenby rotational move ment of the sprocket.

Since the articulated joints of prior art structures are the drivenmembers of the chain assembly they are subjected to severe loads appliedat the sprocket, which loads result in a high rate of external jointwear and/ or fatigue cracking that materially reduces the useful life ofthe chain.

These prior art articulated joints usually comprise a pin connectionwherein the pin is fitted with an external bushing. It is these bushingswhich are subjected to great external wear and fatigue cracking whenengaged by the sprocket.

An additional disadvantage of conventional prior art articulated jointchain structures relates to power losses due to impact forces of thechain drive as it enters upon the driving sprocket. Although very littleinformation has been published on power losses due to impact, it will berecognized from later description in this specification that such lossespresent a serious problem which is greatly reduced by the specialconstruction of the mid-pitch drive of the present invention.

Another advantage of the invention, somewhat related to the impactaspect, resides in the power savings realized from the present mid-pitchconstruction which permits the chain link to rock as it enters upon thedrive sprocket. As will be descibed in particular detail later in thespecification, the construction of the present invention reduces thedistance through which the incoming chain link must 3,567,294 PatentedMar. 2, 1971 travel. Such a reduction results in a decrease inacceleration and deceleration of the incoming chain which in turnresults in a power savings.

A further advantage of the mid-pitch drive construction of the presentinvention over prior art structures relates to a power savings effectedafter impact of the chain With the driving sprocket. In conventionalprior art chain drive constructions the articulated joints are preventedfrom rocking upon the drive spocket because the pins and bushingsforming the articulated joints are the driven members and are engaged inthe notched portions of the sprocket such that they are in effect heldagainst movement. As will be further pointed out in greater detail, suchconventional structures are subjected to frictional power losses due tothe scrubbing action of the articulating bushings against the sprocket.In the case of track-type vehicles this scrubbing action normally occursas the track engages the sprocket when the tractor i in reverse or as itleaves the sprocket when the tractor is in a forward gear, but thesituation may be vice versa depending upon the design. The scrubbingaction also, of course, leads to an extremely high rate of externalbushing wear which materially shortens the useful operational life ofthe chain, since the bushings must be replaced much sooner than would bethe case if this external bushing wear problem could be substantiallyreduced.

The present invention provides a mid-pitch drive construction whichallows for a limited amount of rocking of the chain link upon thesprocket to keep the articulated joint out of engagement with thesprocket during the initial portion of the driving cycle, whichsubstantially eliminates external bushing wear caused by scrubbing ofthe bushing upon the sprocket and also reduces power losses caused bythe scrubbing action. Thus, in the construction of the present inventionthe articulating bushing may eventually bottom out on the sprocket, butonly after articulation is substantially completed and when it is notsubjected to the driving load.

Other objects and advantages of the invention will be apparent from thefollowing description and claims and are illustrated in the accompanyingdrawings which, by way of illustration, show preferred embodiments ofthe present invention and the principles thereof and what is nowconsidered to be the best mode contemplated for applying theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be used and structural changes may be made asdesired by those skilled in the art without departing from the presentinvention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view illustrating onepreferred embodiment of the invention;

FIG. 2 is a side elevation of the embodiment illustrated in FIG. 1;

FIG. 3 is a schematic illustration of a typical prior art construction;

FIG. 4 is a schematic illustration of an embodiment of the presentinvention for comparison with FIG. 3 relative to power loss caused byimpact with a driving sprocket;

FIG. 5 is a schematic illustration of a typical prior art construction;

FIGS. 69 schematically illustrate an embodiment of the present inventionfor comparison with FIG. 5 relative to power loss caused by chordalaction of articulated chain members as they enter upon a drivingsprocket;

FIG. 10 schematically illustrates a prior art construction with regardto wear and power loss caused by scrubbing action;

FIG. 11 schematically illustrates an embodiment of the present inventionfor comparison with FIG. 10;

FIG. 12 schematically illustrates another embodiment of the presentinvention;

FIG. 13 illustrates the manner in which the rocking angle or degrees ofrocking may be calculated for the various embodiments of the invention;and

FIGS. l4l9 illustrate various embodiments of midpitch drive lugconstruction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2 there is shownone preferred embodiment of an improved articulated chain assemblyemploying a mid-pitch drive pin or lug constructed in accordance withthe present invention. The track link section generally shown at 11 issomewhat conventional and comprises a pair of links 12 which areretained in spaced relationship by a pair of track bushings 14 fittedabout the outer diameter of a pair of track pins 16, which are receivedin bores 17 of the links 12. As best shown in FIG. 2, a track shoe 18,provided with the usual grouser 19, extends across the bottom of thelinks 12 and is secured to each of the links by a plurality of bolts 20.

The mid-pitch drive pin or lug is shown at 22 and is disposed at acentral point midway between the track pin bushings 14. In theembodiment of FIGS. 1 and 2, the mid-pitch drive lug 22 is rigidlysecured to the track shoe 18 by a plurality of bolts shown at 23. FIG. 2also illustrates a portion of a driving sprocket 26 and the manner inwhich the mid-pitch lug co-acts with the sprocket 26 which will be morefully explained hereinafter.

In order to properly appreciate the novel mid-pitch drive constructionof the present invention, it will be necessary to compare the structurethereof with prior art conventional articulated chain linkconstructions. It will be assumed for purposes of illustration withrespect to the following material that the tractor is stationary andthat the track is being driven by the sprocket.

As previously mentioned, one of the factors which contributes tohorsepower loss in conventional articulated track link structures is theimpact energy loss caused when the driven articulated link memberstrikes the driving sprocket. FIG. 3 illustrates a typical prior artconstruction which may be compared with the mid-pitch drive constructionof FIG. 4 to illustrate how the construction of FIG. 4 results in areduction of impact energy loss caused when the driven member strikesthe sprocket.

In FIG. 3 a section of track (track link) denoted by the articulatingbushing connections A and B is shown entering upon a driving sprocket.As the articulated section of track enters the sprocket, the trailingbushing portion B moves inwardly toward the sprocket center at a givenvelocity. It will be understood that impact of the trailing bushing B(schematically shown in phantom lines) with the driving sprocket takesplace through a radius R emanating from the center of the leadingbushing A of the articulated joint. Since the radius R is relativelylarge, the impact velocity of the bushing B with the driving sprocket isalso relatively large depending upon the rotative speed of the sprocket.

The illustration in FIG. 4 depicts a mid-pitch drive constructionaccording to the present invention schematically showing the point ofimpact (in phantom lines) of an articulated track section as it entersupon a driving sprocket. It will be observed that in FIG. 4 ascontrasted with FIG. 3, the driven element of the articulated tracksection comprising bushings A and B is the mid-pitch lug member Clocated midway between the bushings A and B. Thus, as the articulatedtrack section of FIG. 4 enters upon the driving sprocket the over-allmotion of the track section is the same as that shown with regard to theconventional track link shown in FIG. 3. However, it should be notedthat contact with the driving sprocket is established through a radiusR/2, which is 4- approximately one-half the distance R denoted in FIG. 3and therefore the impact velocity of the track section shown in FIG. 4is correspondingly reduced as compared with the prior art structureshown in FIG. 3. This, of course, results in a corresponding reductionin power loss caused by the impact of the driven articulated member withthe driving sprocket. In addition there is less chatter of the chain asit enters the sprocket, and a substantial reduction in the noise createdby the chain entering upon the drive sprocket.

Another advantage of the invention, somewhat related to the impactaspect, resides in the power savings realized from the present mid-pitchconstruction which permits a special type of rocking action by the chainlink as it enters upon the drive sprocket. The particular type ofrocking action produced by the present mid-pitch construction produces ahorsepower savings over conventional structures by reducing the chordalaction or the total distance through which the incoming chain link musttravel as it enters upon the driving sprocket.

In FIG. 5 a conventional prior art section of track denoted by thearticulating bushing connection A, B and D, is shown entering upon adriving sprocket. Bushing B has just seated on the sprocket, and as thesprocket rotates the center line of bushing B follows the are describedby the pitch radius. After the bushing B seats on the sprocket and thesprocket continues to rotate the bushing B assumes the phantom lineposition 0 and the effective pitch radius for purposes of calculatingthe velocity of the bushing increases from P to P. Thus, the incomingchain must accelerate and decelerate with each engagement of a newsection of chain and the amount of acceleration and deceleration isrelated to the change in effective pitch radius as each bushing travelsthe path from B to O to A. It will, therefore, be appreciated that theincoming track in such prior art constructions is accelerated anddecelerated with each bushing engagement with concomitant power loss dueto the energy expended during such acceleration and deceleration.

Turning now to FIG. 6, a mid-pitch drive construction according to thepresent invention is schematically shown an instant after the mid-pitchdrive lug C thereof has contacted the driving sprocket. Summation ofmoments about the center of mid-pitch lug C shows a sizable appliedclockwise moment caused by the chain load as shown. A resistivecounterclockwise moment must occur for equilibrium and the bushing Amoves until it bottoms out against the sprocket.

The actual position of an entering mid-pitch drive section of thepreferred construction is shown in FIG. 7. That portion of the trackalready on the driving sprocket will adjust itself accordingly. As thesprocket rotates through the articulation angle which is approximately28 to 30, bushing B takes the position formerly occupied by bushing A.In order for this change of position to take place, some rocking actionmust occur. This rocking is compatible with the applied momentthroughout the articulation angle. For approximately the first 7 ofarticulation a clockwise moment caused by the chain load keeps thebushing B away from the sprocket.

At approximately 7 of rotation there is no applied moment about thecenter of the mid-pitch lug C since the chain load force is applieddirectly through the center of said lug as shown in FIG. 8 wherein thebushing center lines are also shown to be on the pitch radius. From thistime on the chain load force applies a counterclockwise moment about thecenter of mid-pitch drive lug C with bushing B finally bottoming out inthe position formerly occupied by bushing A as shown in FIG. 7. Thecenter line of bushing B therefore does not follow an are described bythe pitch radius, but rather follows a path as shown in FIG. 9.

As shown in FIG. 9, the net effect of the rocking action resulting fromthe mid-pitch drive construction of the present invention causes thebushing B to follow the path shown which, as can be seen, results in asubstantial reduction in the chordal action or distance through whichthe incoming track section must move. FIG. 9 shows by way of comparisonthe distance E which represents the chordal movement of conventionalprior art articulated track link sections as compared with the distanceF which represents the chordal action of mid-pitch drive constructionsaccording to the present invention. The net savings or reduction inchordal action of the mid-pitch drive construction over conventionaltrack link constructions is shown by reference letter G.

It will be understood that the reduction in chordal action or distancethrough which the incoming track section must move results in a decreasein the energy expended for acceleration and deceleration of the tracksection, which ultimately results in a horsepower savings. This powersavings is due to the special construction of the mid-pitch drive of thepresent invention which allows limited rocking action. It should also benoted that the mid-pitch chain construction of the invention definitelyresults in smoother chain action upon entering the driving sprocket thancan be obtained with conventional articulated joint chain constructions.

Thus far in the comparison of the mid-pitch drive construction of thepresent invention with conventional prior art articulated chainconstructions we have emphasized horsepower savings due to a reductionin impact force and also power savings due to a reduction in chordalaction. Another significant advantage, however, of the present mid-pitchconstruction over prior art constructions relates to the reduction ofexternal bushing wear at the articulated joint of the chain.

FIG. 10 illustrates a prior art construction entering upon a drivingsprocket when the tractor is in reverse. The articulated joints ofconventional prior art chain constructions are subjected to a highdegree of bushing wear, especially when the tractor moves in reverse,due to a phenomenon generally referred to as scrubbing.

This scrubbing action consists of relative rotation between the bushingand the notched portion of the driving sprocket as will now be describedwith respect to FIG. 10. Bushing A has just seated on the sprocket andits motion now starts to leave a linear path and enter into acurvilinear path. Note that the reference marks between bushing A andthe sprocket are in line.

As the sprocket rotates through the angle 6 in reverse, the bushing Amoves to the position of bushing B. Note that the reference mark onbushing B has rotated through the angle 4) with respect to the sprocket.This relative rotation o-r scrubbing motion is one of the main factorsin external bushing wear on track bushings. The scrubbing action alsooccurs while going forward, however, chain loads are greatly diminishedby the time the top of the sprocket is reached.

It can be readily observed from FIG. 11 that this scrubbing action issubstantially reduced, if not almost entirely eliminated, in themid-pitch drive construction of the present invention. In FIG. 11 lug Chas just seated on the sprocket. Note that the reference marks betweenlug C and the sprocket are in line. As the sprocket rotates in reversethrough the angle 0, lug C moves to the position of lug K. Even thoughthe lug C undergoes a limited amount of rocking, the reference marks atthe lug K location are still substantially in line indicating thesubstantial elimination of scrubbing action.

It should be noted that the articulating bushings A and B experiencelittle or no external wear because these articulating bushings contactthe sprocket for only a brief period during the critical portion of thedriving cycle when detrimental scrubbing action occurs.

In summary, the mid-pitch drive construction of the instant inventiondrastically reduces external wear on the articulating bushings andresults in a minimal amount of wear on the easily replaced mid-pitchdrive lug member. This is accomplished notwithstanding a slight amountof rocking action which rocking action results in track horsepowersaving due to a reduction of power losses through impact, reducedchordal action, and power saved through the elimination of scrubbingaction.

Various configurations of mid-pitch drive can be designed, however, aswill be noted from the subsequent description, some configurations havedefinite advantages over others. The most important factors in mid-pitchdrive constructions relate to (l) the relationship of the mid-pitchdrive lug center point to the centers of the articulated joints, and (2)the degree of clearance or degrees of rocking provided between thedriving sprocket and the articulating bushings. Either or both of thesefactors can alter the performance of mid-pitch drive construction.

Initially it can be stated that the preferred constructrons are thosedepicted in FIGS. 2 and 6 wherein the center point of the mid-pitchdrive lug is located either on or radially outwardly of a straight linedrawn between the centers of the articulating bushings (bushings 14 inFIG. 2 and bushings A and B in FIG. 6). In other words, the center ofcurvature of the cylindrical top portion of the mid-pitch lugs should belocated on or below a straight line drawn between the centers of thepins at the articulated joints on each side of the lugs. Theseconstructions are preferred because as previously pointed out, and asshown in FIGS. 6, 7 and 8, the incoming bushing B is prevented fromhaving a significant counterclockwise moment about the center point ofmidpitch drive lug C, caused by the force of the chain load, fromengaging with the sprocket during the portion of the driving cycle whendetrimental scrubbing action would occur.

FIG. 12 illustrates a mid-pitch drive lug construction wherein thecenter point of the drive lug C is located radially inwardly of astraight line drawn between the centers of the articulating bushings Aand B". As illustrated therein, summation of forces at the center pointof mid-pitch drive lug C results in an applied counterclockwise momentthereabout due to the force of the chain load. This appliedcounterclockwise moment exists throughout the articulation angle andcauses scrubbing action or external wear on the articulating bushing B".This scrubbing action occurs especially in reverse because the trailingbushing bottoms out against the sprocket near the beginning of thearticulation angle and stays in this position until it reaches theposition formerly occupied by the leading bushing. Thus, while themidpitch drive construction of FIG. 12 possesses advantages overconventional prior art constructions due to a reduction in power lossescaused by impact and reduced chordal action, it is nonetheless not asadvantageous as those mid-pitch drive constructions wherein the centerpoint of the mid-pitch drive lug is located at or radially outwardly ofa straight line drawn between the centers of the articulating bushingsas previously described.

Another extremely important factor in the construction of mid-pitchdrive assemblies in accordance with the present invention relates to therelative size of the articulating bushings with respect to thenotched-out portions of the driving sprocket. It will be understood thatthis relative size factor is one of the determinative factors withrespect to the amount of rocking action about the center point of themid-pitch drive lug. Thus, if the bushings are too large with respect tothe sprocket notches, insufiicient rocking will occur with resultanthorsepower losses due to impact, chordal action and scrubbing action.correspondingly, however, the bushings may be reduced in size to such adegree that excessive wear occurs on the mid-pitch drive lug per sewhich would of course substantially lessen the advantages obtainedthrough the use of said drive lug.

Tests have illustrated that the ideal size for the bushings in order toprovide all the aforementioned advantages of the invention is such thatthe bushings are permitted to rock through an angle which is no greaterthan approximately FIG. 13 illustrates how this rocking angle or degreesrocking may be calculated. FIG. 13 shows a mid-pitch drive constructionin accordance with the present invention wherein the particulararticulated connection in question is shown in a neutral position withrespect to the driving sprocket. The rocking angle is measured between aline drawn between the center point of the lug C and the center of thetrailing bushing B when the bushing is at its maximum outward positionand a line drawn between the center points of lug C and bushing B afterthe bushing has rocked to a bottomed out position with respect to thesprocket. This rocking angle is denoted oz in FIG. 13. Studies haveindicated that the rocking angle should not exceed approximately 20 andpreferably should be about 12 for best results.

FIG. 14 illustrates a modified embodiment of the invention which issimilar to that shown in FIGS. 1 and 2. In FIG. 14 the mid-pitch drivinglug is bolted as at 31 across the track links 32 rather than directly tothe track shoe 34.

FIG. 15 illustrates another embodiment wherein a removable mid-pitchdriving lug 36 is provided with a projection 38 which fits in a slot 40formed in the track shoe 42. The tongue or projection could be formed onthe track shoe rather than the lug and could be of any suitable shape tolend rigidity to the structure.

FIG. 16 illustrates a driving lug embodiment wherein a mid-pitch drivinglug 44 is provided with a removable wear tip portion 46. The tip portion46 may be formed of harder material than the base portion 44.

FIG. 17 illustrates an embodiment wherein the midpitch driving lugcomprises two driving elements 48 one of which is shown for attachmentto link 50 as by bolts 52. This embodiment allows for the provision of agap between the driving elements 48 whereby dirt may escape from betweenthe two driving elements. The track shoe is provided with an aperture toallow the dirt to pass outwardly through the assembly.

FIG. 18 illustrates an embodiment wherein the midpitch driving lug 54 ishollow and is attached to a raised portion 56 of the track shoe by bolts58.

FIG. 19 illustrates an embodiment wherein the midpitch driving lug takesthe form of a pin 60 press fitted into bores formed in the track links62. This embodiment has excellent rigidity due to the nature of thepress fits. It is also possible to retain the pin 60 by suitable hingedjoints to permit the pin to be rotated as wear occurs and then tightenedagain without disassembling the chain.

What is claimed is:

1. In an articulated chain assembly for track-type vehicles wherein anendless track is driven about a driving sprocket and an idler wheel eachsprocket having a plurality of notches of uniform configuration, andwherein each articulated element of said track comprises a pair oflaterally spaced apart links having a track shoe connected thereto andextending across the bottom thereof, and wherein said articulatedelements are hingeably connected to adjacent elements by a cylindricalpin fitted through aligned bores in said links, said pin having anexternal cylindrical bushing fitted thereabout, the improvementcomprising, a mid-pitch driving lug for each articulated element locatedcentrally of said track shoe and generally equidistant the centers ofsaid track pins, said mid-pitch lug having a cylindrical top portionshaped to cooperate with the correspondingly configured notches in thedriving sprocket so that relative rocking movement may occur when themid-pitch lug enters and leaves the notches of the driving sprocket; andwherein the cylindrical bushings at the articulated joints have anoutside diameter which is smaller than the outside diameter of thecylindrical top portion of the mid-pitch lug; said outside diameter ofthe cylindrical bushings having a size relative to the cylindrical topportion of the mid-pitch lug which permits the mid-pitch lug to contactthe notches in the sprocket prior to contact by either cylindricalbushing as each articulated element enters the sprocket and furtherpermits each articulated element of the chain assembly to rock as saidarticulated element enters and leaves the driving sprocket, therebyreducing power losses and reducing external bushing wear.

2. An improved articulated chain assembly as set forth in claim 1wherein said mid-pitch driving lug is provided with a replaceable upperwear surface for contacting the notched portions of said drivingsprocket.

3. An improved articulated chain assembly as set forth in claim 1wherein said mid-pitch driving lug is removably secured to said trackshoe.

4. An improved articulated chain assembly as set forth in claim 1wherein tongue and groove means are provided between said mid-pitchdriving lug and said track shoe for providing a more rigid connectiontherebetween.

5. An improved articulated chain assembly as set forth in claim 1wherein said mid-pitch driving lug is formed in two portions andprovided with a spaced gap between the two portions.

6. An improved articulated chain assembly as set forth in claim 1wherein said mid-pitch driving lug is removably secured to said links.

7. An improved articulated chain assembly as set forth in claim 6wherein said mid-pitch driving lug comprises a pin member press fittedinto bores formed in each pair of laterally spaced apart links.

8. An improved articulated chain assembly as set forth in claim 1 wereinthe mid-pitch driving lugs are removable.

9. An improved articulated chain assembly as set forth in claim 8wherein said mid-pitch driving lug is removably secured to said links.

10. In an articulated chain assembly for track-type vehicles wherein anendless track is driven about a driving sprocket and an idler wheel,each sprocket having a plurality of notches of uniform configuration,and wherein each articulated element of said track comprises a pair oflaterally spaced apart links having a track shoe connected thereto andextending across the bottom thereof, and wherein said articulatedelements are hingeably connected to adjacent elements by a cylindricalpin fitted through aligned bores in said links, said pin having anexternal cylindrical bushing fitted thereabout, the improvementcomprising, a mid-pitch driving lug for each articulated element locatedcentrally of said track shoe and generally equidistant the centers ofsaid track pins, said mid-pitch lug having a cylindrical top portionshaped to cooperate with the correspondingly configured notches in thedriving sprocket, said top portion of the mid-pitch lug extendingupwardly from the track shoe to a height greater than the height of thecylindrical bushings, said cylindrical bushings having a smaller outsidediameter than the diameter of the cylindrical top portion of themid-pitch lug; and wherein the center of curvature of the cylindricaltop portion of the mid-pitch lug is located on or below a straight linedrawn between the centers of the pins at the articulated joints on eachside of said lug, whereby each articulated element is permitted to rockas it enters and leaves the driving sprocket.

11. In an articulated endless track link assembly of the type used on acrawler tractor having a notched drive sprocket, each said linkcomprising: a pair of laterally spaced and vertically disposed side barseach presenting an upper rail portion, parallel pin and cylindricalbushing elements secured to and interconnecting corresponding oppositeends, respectively, of said side bars, a track shoe, connecting meansreleasably securing said shoe to the bottoms of said side bars, and adrive lug releasably secured to said shoe independently of said sidebars and elements and disposed laterally between said side bars andintermediate the axes of said pin and bushing elements, said drive lughaving front and rear convexly curved sprocket engaging surfaces facingin diverging d1- rections and extending laterally substantially the fulldistance between said side bars, the top of said drive lug being of lessheight than said rail portions and lying substantially above the planeformed by said parallel axes, said sprocket engaging surfaces of saiddrive lugs being more gradually curved than said bushing elements andhaving a size and disposition relative to said bushing elements topermit the drive lugs to be engaged by the sprocket notches prior tocontact of said notches by either cylindrical bushing as each linkenters the sprocket.

12. An improved articulated chain assembly as set forth in claim 11wherein said mid-pitch driving lug is provided with a replaceable upperWear surface for contacting the notched portions of said drivingsprocket.

in claim 11 wherein tongue and groove means are provided between saidmid-pitch driving lug and said track shoe for providing a more rigidconnection therebetween.

References Cited UNITED STATES PATENTS 1,186,785 6/1916 Holt 305-58X1,339,786 5/1920 Porter 305-59X 1,377,450 5/1921 Whipple 30552X1,513,459 10/1924 Jett 305-52X 1,678,149 7/1928 Lamb 305-58X 2,598,8286/1952 Phelps 30557 3,359,044 12/1967 BOggs 305-57 13. An improvedarticulated chain assembly as set forth 15 RICHARD J. JOHNSON, PrimaryExaminer

